1. Field of the Invention
Apparatus and methods consistent with the present invention relate to a vehicle control device including an input member drive-connected to a drive power source, such as an engine or a rotating electrical machine, and may also includes a mechanical pump which operates by rotational driving force of the input member, and an electric pump which assists the mechanical pump.
2. Description of the Related Art
In recent years, vehicles having an idling stop function of stopping an engine when the vehicle makes a stop, hybrid vehicles including an engine and a rotating electrical machine (motor or generator) as a drive power source, electric vehicles (electric cars) including a rotating electrical machine as a drive power source, and the like have received attention in terms of energy saving and environmental issues. These vehicles are structured such that the rotation of the drive power source, such as the engine, is completely stopped in a vehicle stopped state, such as during a red light. Therefore, a mechanical pump, which is an oil pump operated by rotational driving force of the drive power source, also stops in the vehicle stopped state, whereby hydraulic pressure of hydraulic oil supplied to a drive transmission system, e.g., an automatic transmission device or a torque converter, decreases. In the case where the vehicle is started from a state where the hydraulic pressure is decreased in this manner, a friction engagement element such as a clutch or brake included in the drive transmission system cannot be engaged appropriately during a period from when the drive power source is started until the hydraulic pressure rises. Thus, situations exist where the vehicle is started in an abnormal manner due to these friction engagement elements suddenly engaging to cause a shock or the like. To try and avoid these situations, a configuration including an electric pump which assists the mechanical pump in order to maintain the hydraulic pressure of the hydraulic oil supplied to the drive transmission system even while the drive power source is stopped has been known (for example, see Japanese Patent Application Publication No. JP-A-2003-172165).
Japanese Patent Application Publication No. JP-A-2003-172165 discloses a parallel hybrid vehicle in which a rotating electrical machine is connected to a crank shaft of an engine, and which is provided with a torque converter and an automatic transmission device between the engine/rotating electrical machine and a wheel. As a friction engagement element, the torque converter includes a lock-up clutch, and the automatic transmission device includes a plurality of clutches and brakes for switching shift speeds. As an oil pump, the vehicle includes a mechanical pump which is operated by the driving force of the engine and the rotating electrical machine as the drive power sources, and an electric pump which operates independently of theses drive power sources. In a state where the engine and the rotating electrical machine are stopped, the vehicle basically supplies the hydraulic oil discharged by the electric pump to the automatic transmission device, and causes the clutch or the brake to engage. However, when the electric pump cannot be driven, such as in cases where the oil temperature of the hydraulic oil is extremely high or extremely low, the electric pump is not operated and the rotating electrical machine is driven to supply hydraulic oil using the mechanical pump. Note that, in Japanese Patent Application Publication No. JP-A-2003-172165, there is no description regarding the operation control of the lock-up clutch of the torque converter.
In the case where a rotating electrical machine is used as the drive power source as with this hybrid vehicle, it differs from a general vehicle, which uses only an engine as the drive power source, in that the driving force can be output from zero rotation to start and run the vehicle. In such vehicles, it has been desired to improve transmission efficiency of the rotational driving force between the drive power source and the wheel, which would improve drive efficiency and energy regeneration efficiency by preventing slippage of a fluid coupling such as the torque converter. It is also desired and that the vehicle be started or run at low vehicle speed with a lock-up engagement element such as a lock-up clutch in an engaged state in order to improve energy efficiency by preventing generation of heat of the hydraulic oil in the fluid coupling. When such vehicles are started or run at low vehicle speed, it is necessary to engage the lock-up engagement element using hydraulic pressure of the hydraulic oil discharged from the electric pump, since the discharge amount of the hydraulic oil from the mechanical pump is not sufficient.
However, in order to run the vehicle in a state where the lock-up engagement element is engaged, and to ensure that a transmission torque capacity greater than or equal to the rotational driving force from the drive power source, a relatively high hydraulic pressure is necessary. However, since the electric pump generally has a lower discharge performance than the mechanical pump, a situation may arise in which the discharge amount of the hydraulic oil from the electric pump becomes insufficient and the necessary hydraulic pressure cannot be ensured. This situation may arise depending on various conditions such as oil temperature of the hydraulic oil, power supply voltage of the electric pump, and the like. For example, in the case where the temperature of the hydraulic oil is extremely low, the viscosity of the hydraulic oil increases and the discharge amount of the hydraulic oil from the electric pump decreases. On the contrary, in the case where the temperature of the hydraulic oil is extremely high, the viscosity of the hydraulic oil decreases to increase the leakage amount from respective sections of supply destinations of the hydraulic oil, and the discharge amount of the hydraulic oil from the electric pump becomes relatively insufficient. When an attempt to engage the lock-up engagement element is made in a state where the discharge amount of the hydraulic oil from the electric pump is insufficient, there is a possibility that an engagement failure such as slippage occurs, a shock due to sudden engagement occurs, or the like. On the other hand, when the electric pump having a high discharge performance is used to prevent such a situation, there are problems that the pump increases in size, increases in weight and volume and that energy consumption (electrical power consumption) necessary for the operation of the electric pump increases.